Rack gear with improved method of making



Jan. 20, 1959 PROEFKE 2,869,339

RACK GEAR WITH IMPROVED METHOD OF MAKING Filed Dec. 27, 1954 INVENTOR.

va/195k! PROEFAF.

l i l RAGK WITH IMPROVED METHOD *OF MAKING Lawrence Proefke, Detroit, Mich.

Application Decemberfl,1954, Serial No. 477,748

' 1- Claim. (Cl. 74-462) This invention relates to a-novel rack gear construction and a novel method of manufacture.

It' isthe object of Lthepresent invention to provide a rackgear construction which is achieved by grinding accurately the gear segments or teeth in a thread-grinding machine. a

It is the further object of the presentinvention to provide an extremely accurate rack gear construction wherein the gear segments areof crown shape or tapered and wherein the plane-surfaces forming each side of the gear teeth are formed by a pair of angularly related flat ground surfaces and wherein the angular relationship is'slight.

It is the further object of the present invention to-provide a novel method of manufacturing a rack gear wherein the teeth of the rack. gear are blanked 'by an initial machining operation' and thereafter accurately ground to the proper size and shape in athread-grinding machine. The present process or method involves a new approach to-the art of producing accurately ground modified rack teeth. This method produces racks by regarding them as a small section of a large screw thread which is readily ground on a thread-grinding machine. In the new method advocated herein, two intersecting spiral paths of opposite hand, but of the same lead, are employed in the grinding procedure to thereby define the rack teeth.

The resulting rack tooth thus generated will develop the desired proportions through any given vertical section. The tooth will be crowned and have the effect of having no offset angle. This means further than any vertical section taken through a particular tooth to the right or the left of a central section will produce slightly smaller proportions and will have the effect of giving contact to a mating gear only through the central section. The crowning effect obtained will permit effective rolling action of a spur or helical gear with respect to a rack thus ground, even if there is a certain amount of misalignment between the two gears.

These and other objects will be seen from the following specification and claims in conjunction with the appended drawing in which:

Fig. l is a fragmentary plan view illustrating the supporting fixture for a pair of rack gear-blanks as journaled within a thread-grinding machine which is fragmentary and diagramatically illustrated.

Fig. 2 is a left side elevational view thereof.

Fig. 3 is a partially broken-away fragment of a rack gear produced by the present method, shown in perspective.

Fig. 4 is a fragmentary side elevational View thereof; and

Fig. 5 is a fragmentary plan view thereof.

It will be understood that the above drawing illustrates merely one preferred embodiment of the invention and method of manufacture, and that other embodiments and methods are contemplated within the scope of the claims hereafter set forth.

Referring to the drawing, Fig. 1 fragmentarily and dia- United States Patent 2,869,389 Patented .Jan. 20, 1 959 a pairof rack gear blanks 21 and 22 which are secured thereto in the manner hereafter described.

The thread-grindingmachine ,includesa conventional lead screw construction whereby a longitudinally adjustable carriage maybe fed. The centers lland-IZ including the driving means for rotating the bracketI-S are carried by such carriageso that while the bracket 15 is continuously rotated in one direction, there will also be a longitudinal feed of the workpiece supporting bracket, all in a conventional manner and with respect. to the power driven thread-grinding wheel i3driven by motor-14.

The bracket 15 has at its opposite endsa pair of centrally' arranged outwardly projecting aligned mounting studs 16 and 17 which register with'thecenters 11 and 12, one of which is adapted to effect-a rotating and driving relation to-bracket-IS in 'a conventional manner, the opposite ends of projections 16 2111(1'17 being centrally apertured as at 18, Fig. 2. -It is submitted that-Pig. 1 is purely a diagrammaticalillustration.of the driving and supporting portion of :a thread 'grinding machine and, naturally, it is contemplated that one of the centers 11 and 12 will effect a rotating drive to the said blank supporting fixture 15.

-Said-fixture includes upon its opposite sides'a pair of elongated outwardly directed laterally displaced oppositely arrangedblank mounting plates 19 which register with and cooperate with the elongated shouldersZil formed in the central portion of bracket .115 for cooperatively and supportably receiving the corresponding elongated edgeof thetwo rack gear blanks 2'1 and 22.

For the purpose of securing said blanks-upon the supports-19,-thesaid supports areprovidedwwith a series of elongated transverse apertures 112i? -which permit .the .insertion theretbrough of the securing bolts 24 which threadedly engage the blanks 21 and 22 through the interiorally threaded apertures 25 formed in said blanks, as illustrated in Figs. 1 and 4.

In the initial step of forming the said rack gears, there is formed within the blank a series of gear tooth segments 'by an initial machining operation as at the spaced points 26, Fig. 4, to initially form the gear teeth of the rack along the outer edges 27 of said blanks. The said blanks project outwardly from the fixture supporting plates 19, as indicated at 28, Fig. 1, and are so arranged within the thread-grinding machine as to be operatively engaged by the pro-formed periphery in thread-grinding wheel 13 which is power driven.

in operation and in forming the finally ground rack gear teeth, the grinding wheel 13 is initially set to a predetermined lead angle such as shown in Fig. 1. The motor 14 is energized and the blank mounting fixture 15 is continuously rotated under power and in view of the conventional carriage lead screw will at the same time be effecting a continuous longitudinal feed in one direction relative to said grinding wheel to thereby form a discontinuous spiral-path relative to the two gear blanks 21 and 22, as is apparent that the said grinding wheel will be out of contact with the said blanks throughout certain periods of their rotation. As the said gears have been initially blanked out as at 26, Fig. 4, it is merely necessary for the thread-grinding wheel 13 to now accurately grind the surfaces of the respective gear teeth which in their finally formed condition are shown at 30 in Fig. 3.

With the grinding wheel 13 set at the angle shown in Fig. 1, the initial pass of the blanks with respect to the grinding wheel will effect a grinding of the surfaces 33 and 34, being complemental surface portions of adjacent.

rack gear teeth in view of the inclination or lead of the said grinding wheel. Thus in the initial pass these surfaces 33 and 34 will be accurately ground as to all gear There are then provided additional passes of the gear blanks with respect to the grinding wheel during which period the other surfaces 31 and 32 of adjacent pairs of gear teeth 30 will be formed, and here also these surface elements 31 and 32 are in parallel relation.

The teeth so formed will be crowned and will correspond to the cross sectional shape given to the periphery of the grinding wheel 13. v

Fig. 3 exaggerates slightly the exact angular relationship between the surfaces 31 and 33 upon one side of the gear tooth and surfaces 32 and 34 upon its opposite side. While there is a definite angular relationship between the said plane surfaces to thereby define a slight ridge 35 at the central portion of each tooth, nevertheless, the angular lead is quite small and, consequently, the angular relationship between the intersecting plane surfaces is small, and hardly noticeable.

This means that when a driving relationship is established between the tooth 30 and a pinion for illustration, that initial contact with the pinion and the teeth 30 will be at the points 35 or ridges. After some use, however, this ridge will be practically worn down.

The teeth so formed as at 30 are tapered or have a crowned effect as indicated at 36, in Fig. 3, and, of course, the shape of the said crowning depends entirely (1) Crowned rack gear teeth can be ground on threadgrinding machines which will thus produce rack gears faster than conventional methods.

(2) Crowned rack gear teeth can be accurately ground.

(3) The crowning effect obtained will permit effective rolling action of a spur or helical gear with respect to a rack thus ground, even if there is a certain amount of misalignment between the two gears.

Having described my invention, reference should now be had to the claim which follows for determining the scope thereof.

I claim:

A rack gear comprising an elongated body substantially rectangular in cross section and a series of longitudinally spaced teeth of crown shape in vertical crosssection, each tooth including on each side thereof a pair of ground plane surfaces, arranged at an obtuse angle to each other, and with a plane surface on one side of a tooth towards one end being parallel to a diametrically opposite surface of an adjacent tooth at its opposite end, said teeth being formed as segments of a pair of intersecting spirals of the same but opposite lead ground into said body, said angularly related surfaces on each side of a gear tooth defining central ridges upon opposite sides of each tooth.

' References Cited in the file of this patent UNITED STATES PATENTS 5,647 Semple June 27, 1848 618,272 Johnson Jan. 24, 1899 2,128,815 Guest Aug. 3, 1938 2,335,504 Gazda Nov. 30, 1943 2,346,865 Pelphrey Apr. 18, 1944 2,347,998 Drummond May 2, 1944 FOREIGN PATENTS 561,714 Great Britain June 1, 1944 

